Semiconductor IC with dual groove isolation

ABSTRACT

A bipolar type of semiconductor integrated circuit device is provided with U-shaped grooves which are formed by cutting a main surface of a semiconductor body to form isolation regions between bipolar transistors. A silicon oxide film can be formed in the U-shaped grooves by thermal oxidation simultaneously with the formation of a silicon oxide film used to form isolation regions between each collector contact region and base region. No separate step is needed for forming the silicon oxide film between the collector contact region and the base region. The thickness of the silicon oxide film can be controlled, and has a sufficient thickness even at its two edges, i.e., at its boundaries with the U-shaped grooves, so that the bipolar transistors exhibit good electrical characteristics. Namely, the collector resistance thereof does not increase, and the breakdown voltage at the pn junction between the collector region and the base region does not decrease. The U-shaped grooves can each comprise narrow and deep sub-grooves, with thick oxide films formed on the surfaces of the sub-grooves and a thick oxide film formed on a surface of an area between the sub-grooves, and with wiring formed on the oxide on the area between the sub-grooves.

The present application is a continuation-in-part of application Ser. No. 824,929, filed Jan. 31, 1986, now abandoned, which was a continuation application of application Ser. No. 536,519, filed Sept. 28, 1983, now abandoned, and is a continuation-in-part of application Ser. No. 670,976, now abandoned, filed Nov. 13, 1984.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and semiconductor fabrication techniques. More particularly, the present invention relates to a semiconductor device in which a plurality of semiconductor elements and/or regions are electrically isolated from each other by grooves formed in a semiconductor substrate, and to a technique of isolating elements which can be effectively utilized for the formation of element-isolating regions in a semiconductor integrated circuit device.

Elements in semiconductor integrated circuit devices are isolated by a pn junction isolation method using diffusion layers or by an oxidation film isolation method utilizing local oxidation films formed over the surface of the substrate. With these isolation methods, however, the widths of the isolation regions are relatively wide. As the size of the elements becomes smaller, therefore, the isolation regions occupy proportionally larger areas. This makes it difficult to obtain LSI (large-scale integrated) circuits in a very densely integrated form. The applicants have therefore proposed an isolation technique called the U-groove isolation method in which portions that act as isolation regions between active regions of elements are cut to form U-shaped grooves (moats or trenches, hereinafter referred to as U-grooves). A silicon dioxide film is formed within the U-grooves which are then filled with polycrystalline silicon. These form element-isolating regions.

This technique has been disclosed in, for example, the journal "NIKKEI ELECTRONICS", March 29, 1982, No. 287, pp. 90-101.

Such isolation method of isolating semiconductor devices by forming grooves in a semiconductor substrate and filling the grooves with insulative material requires a smaller space and attains a smaller parasitic capacitance than a pn junction isolation method and it is suitable to a high integration and high speed LSI. However, in this method, if the grooves on the surface after the insulating material has been filled in the grooves are wide, it is difficult to flatten the surface and a very complex process is required to flatten the surface. Accordingly, the width of the grooves is restricted to facilitate the flattening. However, when the width of the isolation grooves is restricted, parasitic active regions are created in the devices on the opposite sides of the groove and wiring capacitance increases. This results in a reduction of operation speed of the circuit.

The fact that a propagation delay time of 0.3 ns/gate with an isolation capacitance of 0.2 pF is attained by forming grooves in a semiconductor integrated circuit substrate is disclosed in an article Japanese Journal of Applied Physics, Volume 21 (1982) Supplemental 21-1, pages 37-40.

U.S. Pat. No. 4,396,460, directed to subject matter invented by the authors of the above article and filed on May 21, 1982, discloses a method for flattening an area of a wide isolation groove.

Bipolar transistors are the main elements in the construction of a bipolar type of semiconductor integrated circuit device. However, bipolar transistors must be isolated from each other by U-grooves when they are very densely arranged on a semiconductor substrate.

To reduce the size of a bipolar transistor, however, an n⁺ -type semiconductor region that acts as a collector contact region must be isolated by an insulating material from a p⁺ -type base region.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductor device which can reduce a stray capacity of wiring on an inactive region without complicating the manufacturing process.

The isolation in accordance with the present invention uses a combination of a pair of narrow and deep grooves, oxide films (e.g., thick oxide films) on the surfaces of the grooves, and an oxide film (e.g., thick oxide film) on a surface area between the grooves.

As another aspect of the present invention, the inventors have discovered that a problem arises when an attempt is made to simultaneously satisfy the two requirements of providing bipolar transistors isolated from each other by U-grooves and providing an n⁺ type semiconductor region acting as a contact region and a p⁺ -type base region isolated from each other by an insulating material.

When deep U-grooves isolating individual transistors and shallow U-grooves isolating each base region and collector region are used, the manufacturing process is complicated, and increased collector resistance makes the switching speed drop.

When U-grooves are used to isolate individual transistors, and when a field oxide film is used to isolate each base region and collector region, the breakdown voltage at the pn junction between the base region and the collector region drops due to "bird's beaks" formed in the field oxide film.

Accordingly, an object of this aspect of the present invention is to increase the degree of integration of semiconductor integrated circuit devices (e.g., bipolar semiconductor integrated circuit devices), without impairing their electrical characteristics.

A further object is to improve the electrical characteristics of semiconductor elements formed on a semiconductor body.

A further object is to provide a process of manufacturing a semiconductor integrated circuit device in which semiconductor regions that act as collector contact regions and base regions are sufficiently isolated from each other, without increasing the number of processing steps.

A further object is to provide a process of manufacturing a semiconductor substrate, for use in forming integrated circuit devices having increased integration with no impairment of electrical characteristics, and the substrate and integrated circuit deice formed thereby.

This aspect of the present invention is described below briefly.

In a bipolar type of semiconductor integrated circuit device in which elements are isolated by U-groove isolation regions, an oxide film providing isolation is formed between a semiconductor region that acts as a collector contact region and a base region, simultaneously with the formation of a silicon oxide film within the U-shaped isolation grooves. This eliminates the necessity of providing a step of forming a new isolation oxide film. The thus-formed isolation oxide film does not reach the n⁺ -type buried layer, and possesses sufficiently thick end portions even at its boundaries with the U-groove isolation regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 8 show manufacturing steps of one embodiment of the present invention;

FIGS. 9 to 12 show manufacturing steps of a second embodiment of the present invention;

FIGS. 13 and 14 show manufacturing steps of a third embodiment of the present invention;

FIGS. 15 to 17 show manufacturing steps of other embodiments of the present invention;

FIGS. 18 to 21, 23 and 25 to 33 are sections showing the steps of manufacturing a bipolar type of semiconductor integrated circuit device;

FIG. 22 is a plan view of a bipolar type of semiconductor integrated circuit device during manufacture; and

FIG. 24 is a section through the device of FIG. 22.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment concerning the manufacture of a bipolar integrated circuit is now explained.

As shown in FIG. 1, a collector buried layer 2 of a thickness of 0.5-3 μm is formed in a surface of a Si substrate 1 having a plane orientation (100), a Si epitaxial layer 3 (having a thickness of 0.5-3 μm, preferably 1-1.5 μm) which serves as an active region of a transistor is formed thereon, the surface thereof is oxidized to form a SiO₂ film 4 having a thickness of 0.05-0.10 μm, and a Si₃ N₄ film 5 is formed thereon by a well-known CVD process.

Then, the Si₃ N₄ film 5 at areas 6, 8 and 28 in which grooves are to be formed as shown in FIG. 2 are selectively removed by a dry-etching process using a conventional photo-etching method, and the surface is again photo-etched to remove the exposed areas 8 and 28 of the SiO₂ film 4 while leaving the SiO₂ film 4 at an area of a shallow isolation groove 6 and at a center area 7 of a wide isolation area 8-7-8 having a width of 0.5 to 2000 μm to form openings 8 and 28 at areas in which deep device isolation grooves are to be formed. The widths of the openings 6, 8 and 28 are preferably equal to or narrower than the depths of the grooves to be described later, from a standpoint of a subsequent flattening process.

Then, as shown in FIG. 3, generally vertical grooves 9 are formed in the Si layer 3 by a well-known dry etching process such as a reactive sputter etching using the SiO₂ film 4 of the areas 6 and 7 as a mask. Before dry etching, the SiO₂ film 4 may be etched to widen the openings 6, 8 and 28 to diverge the tops of the grooves upward to enhance the flatness of the surface. This shape is hereinafter referred to as a Y-shaped groove. The flatness of this Y-shaped groove is advantageous to a multi-layered integrated circuit structure having an element or wiring stacked on the other element. The groove 9 extends through the Si epitaxial layer 3 and into the collector buried layer 2 by approximately 0.5 μm.

The exposed areas of the SiO₂ films 4 and 6 between the grooves 9 are removed by a wet etching process using buffered HF as an etchant (FIG. 3).

Then, the Si films 3, 2 and 1 are again dry-etched to form isolation grooves 10 which are shallower than the collector buried layer 2 and deep device-to-device isolation grooves 11 which extend into the collector buried layer 2 (FIG. 4). The depth of the grooves 11 is 1.5-6.5 μm depending on the thicknesses of the collector buried layer 2 and the Si epitaxial layer 3.

The exposed areas of the Si films 1, 2 and 3 are then oxidized using the Si₃ N₄ film 5 as a mask to form a SiO₂ film 12 having a thickness of approximately 400 nm. After the Si₃ N₄ film 5 used as the mask has been removed, a Si₃ N₄ film 13 having a thickness of approximately 100 nm is formed on an entire surface, and a thick poly-Si layer 14 is formed by CVD process to fill the grooves (FIG. 5).

The poly-Si 14 is then etched by isotropic etching (either dry or wet) until the surface of the Si₃ N₄ film 13 is exposed to flatten the surface (FIG. 6).

Then, the surface of the poly-Si 14 is oxidized to form a SiO₂ film 15 having a thickness of approximately 400 nm and the exposed areas of the Si₃ N₄ film 13 are removed and a Si₃ N₄ film 16 having a thickness of approximately 100 nm is formed on the entire surface. Thus, the interdevice and device-to-device isolation processes are completed (FIG. 7).

Then, a collector take-out region 17, a base region 18 and an emitter region 19 are formed by diffusion or ion implantation, and passivation film 16 formed in the step of FIG. 7 and the SiO₂ film 4 are selectively etched using a mask to form a base electrode 20, an emitter electrode 21 and a collector electrode 22 to complete a transistor (FIG. 8). A conductive line 23 deposited above the filling poly-Si layer is also shown in FIG. 8.

The bipolar LSI thus constructed has two thick oxide layers 12 and 15 and two Si₃ N₄ layers 13 and 16 in the interdevice isolation area 24. Let us consider a parasitic capacitance between the conductive line 23 and the substrate 1. The dielectric constant of the Si₃ N₄ films 13 and 16 is approximately 2 to 4. The thicknesses of the films are about 100 nm. The poly-Si layer 14 is sandwiched between the films. This dielectric constant is larger than that of the SiO₂ film, whose relative dielectric constant is approximately 2.8. Accordingly, the contribution of the Si₃ N₄ film of 100 nm thickness to the capacitance corresponds to that of the SiO₂ film of about 70 nm thickness. Accordingly, if the poly-Si film 14 is disregarded, two pairs of Si₃ N₄ -SiO₂ films have a capacitance corresponding to the SiO₂ film having a thickness of 940 nm, that is, approximately 1×10⁻⁵ pF/μm². A single pair of the 100 nm thick Si₃ N₄ film and the 50 nm thick SiO₂ film has a capacitance corresponding to the SiO₂ film having a thickness of 120 nm, that is, approximately 9×10⁻⁵ pF/μm². Accordingly, the parasitic capacitance of the present embodiment is one-ninth of that of the prior art device. An electric resistance of the poly-Si layer 14 of FIG. 8 is in the order to 10 MΩ-cm but it may be considered that a depletion layer is formed in the poly-Si layer 14 by an electric field applied thereto to reduce the parasitic capacitance.

In the embodiment of FIG. 8, the bottoms 25 of the two shallow grooves reach the surface of the collector buried layer 2. The thickness of the poly-Si layer 14 depends on the thicknesses of the collector buried layer 2 and the Si epitaxial layer 3.

When it is not required that the shallow grooves extend to the collector buried layer, the amount of etching of the Si layer 14 for the shallow grooves in the step of FIG. 4 may be reduced. The etching step of FIG. 4 for forming the shallow grooves may be omitted. The thickness of the poly-Si layer 14 is 0-5.5 μm. By selecting the depth of the shallow grooves 10 to approximately one-half of the thickness of the SiO₂ film 12, the flatness of the surface 26 relative to the other areas is attained by thermal oxidation as shown in FIG. 9. FIGS. 10-12 show manufacturing steps for a second embodiment shown in FIG. 9. They correspond to FIGS. 4-6, respectively. The Si epitaxial layer 3 in the wide isolation region 7 shown in FIG. 10 is not etched. FIGS. 11 and 12 show the same steps as those shown in FIGS. 5 and 6, respectively. The thickness of the SiO₂ film 12 shown in FIG. 11 may be slightly larger than the thickness of 400 nm of the SiO₂ film shown in FIG. 5, that is, it may be 500-600 nm. As a result, a stray capacitance which is approximately 1/4.5 to 1/5 of that of the 120 nm thick SiO₂ film is attained. The collector buried layer 42 shown in FIGS. 8 and 9 is isolated by the deep groove from the other collector buried layer 2.

The device isolations in the first and second embodiments were applied to devices of a bipolar semiconductor integrated circuit and to the peripheries of bonding pads (approximately 100 μm×100 μm) and the underlying areas of the wirings from the bonding pads to the circuit components. A propagation delay time was 0.2 ns/gate. It shows an improvement of 50% over the propagation delay time of 0.3 ns/gate shown in the article of the JJAP.

FIGS. 13 and 14 show a third embodiment. The shallow groove 10 shown in FIG. 10 is formed for the interdevice isolation. In FIG. 13, the step of forming the shallow groove 10 is omitted and the interdevice isolation is attained by a SiO₂ film 32 having a thickness of 400-600 nm formed by thermal oxidation. FIG. 14 shows a collector diffusion region 34, an emitter diffusion region 33 and a base diffusion region 35 having their diffusion regions delimited by the SiO₂ film 32.

FIG. 15 shows a fourth embodiment in which the width of the interdevice isolation region of the above embodiment is widened to 10 μm or longer. The surface has no step and has a smooth contour.

FIG. 16 shows a fifth embodiment.

The cross-sectional shape of the groove is not limited to the U-shape shown in the embodiment but a V-shape or a Y-shape or combination of the three shapes may be used. By over-etching the SiO₂ film 4 shown in FIG. 2 and isotropic-etching it by alkaline etchant (KOH or hydrazine) in an early stage of Si etching to form a Y-shaped slope at the top of the deep cylindrical groove to widen the top outward, the flatness of the surface is improved as shown in FIG. 16.

In the above embodiments, the filling material 14 for the isolation grooves is the poly-Si. Alternatively, other insulating material such as SiO₂ or Si₃ N₄ may be used. The thickness of the Si₃ N₄ film for masking or passivation is not limited to 100 nm but it may change between 30 nm and 500 nm.

FIG. 17 shows an embodiment of a MOS LSI in accordance with the present invention. A source 51, a drain 52, a poly-Si gate 53 and a thin gate oxidation film 50 under the gate 53 are similar to those of a conventional MOSFET structure. An Al conductive wire 58 is contacted to the drain 52 and extends onto a SiO₂ film 56 having a thickness of 200 nm to 1.0 μm between two grooves 55 having a depth of approximately 0.3 to 1.0 μm, and onto a passivation layer 57 (such as PSG).

Noting FIG. 14 as discussed previously, particularly the grooved device-to-device, and oxide layer intradevice, isolation thereof, FIGS. 18 to 33 illustrate an embodiment in which one aspect of the present invention is adapted to a bipolar type of semiconductor integrated circuit device having specific device-to-device and intradevice isolation, with the manufacturing steps shown sequentially.

According to this embodiment, a semiconductor body 124 (note FIG. 18) is first prepared. Holes for the formation of buried layers are formed at suitable positions in a silicon oxide film formed over a semiconductor substrate 101 that consists of p-type monocrystalline silicon. Using the silicon oxide film as a mask, n-type impurities are thermally diffused into the substrate 101 to form a local n⁺ -type buried layer 102. After the silicon oxide film is removed, an n⁻ -type epitaxial layer 103 is grown onto the substrate 101 by a vapor growth method, to provide the semiconductor body 124.

A silicon oxide film (SiO₂ film) 104 and a silicon nitride film (Si₃ N₄ film) 105 are formed, utilizing conventional processing steps, on a main surface of the semiconductor body 124.

The silicon nitride film 105 is removed from portions where wiring will be formed around the periphery of the chip. Using the silicon nitride film 105 as a mask, the main surface of the substrate 101 is cut by a conventional isoplanar technique, followed by thermal oxidation, to form a field oxide film of a thickness of between 1 μm to 1.2 μm, as shown in FIG. 18. Such a field oxide film 106 is formed using conventional processing steps used to form such field oxide films. Since the field oxide film 106 is so thick, it is possible to reduce the electrostatic capacity of the wiring provided in the wiring regions.

The silicon nitride film 105 is removed, and another silicon nitride film 125 made, e.g., by chemical vapor deposition (CVD) is formed over the whole surface of the substrate. An exemplary thickness for such a silicon nitride film 125 is 3000 Å.

The silicon nitride film 125 is removed by etching (e.g., wet or dry etching) from portions at which isolation regions will be formed, i.e., from the peripheries of bipolar transistors and from regions between the base region and the collector contact region of each transistor. Using the silicon nitride film 125 as a mask, the surface of the semiconductor body 124 is locally oxidized by heating. Silicon oxide films 126a and 126b of a thickness of between 3000 to 3500 Å are then formed over the portions at which the isolation regions will be formed, as shown in FIG. 19. The isolation region, base region, collector contact region, and the isolation region between the base region and the collector contact region are defined by the silicon nitride film 125.

The exposed oxide films 126a are removed by wet etching (using, e.g., conventional techniques), without removing the remaining portions of the silicon nitride film 125, after the region between the base region and the collector contact region is covered with a photoresist film 127. Removal of the exposed oxide films 126a provide grooves having a depth of 500-1000 Å, as an example. The silicon oxide film 126b is left between the base region and the collector contact region, and is used as a mask for the etching of the semiconductor body 124 and for the implantation of ions. After the photoresist film 127 is removed, the openings of the grooves are tapered, as shown in FIGS. 20 and 21, by etching with hydrazine. Such etching with hydrazine provides deepened grooves having a depth of, e.g., 5000-6000 Å, with a taper of 55° from the main surface, for example. The silicon oxide film 126b is not etched by the hydrazine. If the surface of the semiconductor body 124 has been sufficiently tapered after the silicon oxide films 126a have been removed, etching with hydrazine is not necessary. Such tapering is provided to prevent dislocations from being generated in the oxidation process for forming film 109 (FIG. 25).

Deep grooves 107 of, e.g., 4 μm depth are formed by dry etching using the silicon nitride film 125 and silicon oxide film 126b as masks so that the grooves reach as far as the substrate 101, as shown in FIG. 22. The etching reduces the thickness of the silicon oxide film 126b of about 2000 Å.

Using the silicon nitride film 125 and silicon oxide film 126b as masks, boron ions are implanted into the bases of the U-grooves 107 (at a dose of 10¹⁴ atoms/cm², and an energy of 30-40 KeV, for example), and p⁺ -type channel-stopper layers 108 are then formed as shown in FIG. 23 by heat treatment (for example, at 1000° C. for 10 minutes). The boron ions are not introduced into the surface of the semiconductor substrate 124 in the regions where the silicon oxide film 126b has been formed. The breakdown voltage at the pn junction between the base region and the collector region is increased by the introduction of the boron ions. If the silicon oxide film 126b is about 1000Å thick, it is capable of preventing the boron ions being introduced into the semiconductor body 124.

Using the silicon nitride film 125 as a mask, the surface of the semiconductor body 124 is thermally oxidized, which forms a silicon oxide film 109 of a thickness of about 6000 Å in each U-groove 107. Although not limiting, such a film 109 can have a thickness of 4000-8000 Å. Since the nitride film 125 has been removed from the portion between the base region and the collector contact region, a relatively thick isolation oxide film 110 of a thickness of between about 7000 to 8000 Å is formed at this portion. The thickness of the silicon oxide film increases since oxygen reaches the surface of the semiconductor body 124 through the silicon oxide film 126b. The silicon oxide film 110 is thicker than the silicon oxide film 109 by the thickness of the silicon oxide film 126b.

The device in this state is shown in FIGS. 24, 25 and 26, where FIGS. 25 and 26 are sections taken along the lines B--B and C--C of FIG. 24, respectively. In FIG. 24, dot-dash lines 121a, 121b and 121c denote the positions of contact holes that will be formed in a subsequent step.

As shown in FIG. 26, the silicon oxide film 110 has end portions that continue from the silicon oxide film 109, at the same thickness, so that the base region and the collector contact region are reliably isolated from each other. No stress concentration which would generate crystal defects occurs at the boundaries between the U-grooves 107 and the silicon oxide film 110.

A silicon nitride film is deposited over the whole surface of the semiconductor body 124 by a CVD method or the like so that a silicon nitride film 111 (up to a thickness of, for example, 500 Å) is formed over the oxide film 109 within the U-grooves 107, as shown in FIG. 27.

Polycrystalline silicon is deposited thickly over the whole surface of the semiconductor substrate 124 by the CVD method, so that the U-grooves 107 are filled with polycrystalline silicon. The layer of polycrystalline silicon on the surface of the substrate is removed by dry etching to flatten the surface, leaving polycrystalline silicon 112 within the U-grooves 107, as shown in FIG. 28. Materials for filling the U-grooves 107 are not limited to polycrystalline silicon, and can also include, e.g., SiO₂.

Using the silicon nitride film 125 as a mask, the surface of the polycrystalline silicon 112 in each U-groove is thermally oxidized to form a silicon oxide film 113 to a thickness of 500-6000 Å, e.g., 6000 Å, on top of the polycrystalline silicon 112. Then, as shown in FIG. 29, the silicon nitride film 125 is removed from the collector contact region, using conventional wet or dry etching for removal of silicon nitride films. Using the remaining silicon nitride film 125 as a mask, n-type impurities are implanted and are thermally diffused, as conventionally done, therein to form an n⁺ -type semiconductor region that acts as the collector contact region.

The silicon nitride film 125 is removed using the silicon oxide film 113 as a mask, and p-type impurities are implanted into the whole main surface of the semiconductor body 124 to form a base region, as conventionally done. A new silicon nitride film 115 is formed over the semiconductor body 124, and a p⁺ -type semiconductor region 116 that acts as a base region is formed by a heat treatment. Then, as shown in FIG. 30, the silicon nitride film 115 is removed from the portion that will be the emitter region.

The oxide film 104 is removed by etching from the surface of the portion that will be the emitter region, and polycrystalline silicon is thinly deposited (e.g., a thickness of 2500 Å) by a CVD method over the whole surface of the semiconductor body 124. Using conventional processing techniques, n-type impurities such as arsenic ions are implanted into the polycrystalline silicon layer, and are then diffused from the polycrystalline silicon layer by a heat treatment to form an n⁺ -type semiconductor region 118 that acts as the emitter region. A polycrystalline silicon electrode 119 is left on the emitter region 118 by a photolithographic technique, as shown in FIG. 31.

In this device, the emitter region 118 is formed by the diffusion of ions from the polycrystalline silicon layer. It is, however, also possible to implant ions and effect a heat treatment to form the emitter region prior to the depositing of the polycrystalline silicon. Furthermore, the emitter region can be formed by implanting and diffusing ions, and by making the ions diffuse from polycrystalline silicon, before depositing the polycrystalline silicon electrode.

A PSG film (phosphosilicate glass film) is formed by a CVD method over the semiconductor body 124, to form an intermediate insulating film 120. Using a photoresist film as a mask, contact holes 121a to 121c are formed by etching, as shown in FIG. 32, to form the contact holes to the base region, emitter contact and collector region.

A wiring material such as aluminum is vaporized onto the whole surface of the semiconductor body 124, and aluminum electrodes 122a to 122c as well as aluminum wiring are formed by a photolithographic technique. A final passivation film 123 such as an SiO₂ film is then formed, as shown in FIG. 33.

FIG. 33 shows only one bipolar transistor with an epitaxial layer 103 to its right instead of other transistors. This is also true for FIGS. 29 to 32.

In this embodiment, the isolation oxide film 110 (that is, intradevice isolation) is formed between the collector contact region 114 and the base region 116, simultaneously with the formation of the silicon oxide film 109 in each U-groove isolation region. Therefore, no separate step is required for the formation of the isolation oxide film 110. Furthermore, when each collector region 114 and base region 116 are isolated from each other by a shallow U-groove, it is necessary to cut the U-grooves using two steps. According to this embodiment, however, the U-grooves 107 can be formed by a single step, simplifying the process.

The isolation oxide film 110 is formed simultaneously with the formation of the silicon oxide film 109, so that the isolation oxide film 110 is formed nearly uniformly from the central portion to the edge portions thereof, as shown in FIG. 26. On the other hand, when the silicon oxide film 109 and the isolation oxide film 110 are formed by separate steps, the boundaries between both edges of the oxide film 110 and the U-groove isolation region 107 become so thin that the breakdown voltage at the junction between the base region and the collector region drops. According to the present embodiment of the present invention, on the other hand, the breakdown voltage does not decrease but is kept sufficiently high.

It is easier to control the thickness of the oxide film 110 than the depth of the U-shape isolation regions, so that variations in the electrical characteristics of the transistors can be reduced. The method in which the collector contact region 114 is isolated by a U-groove isolation region from the base region 116 has the disadvantage that, as the U-groove reaches the buried layer 103 through the epitaxial layer 102, the collector resistance increases. When the U-groove is shallow, on the other hand, the breakdown voltage at the junction between the base region and the collector region drops. According to this embodiment, however, the electrical characteristics of the transistors are greatly improved.

In this embodiment, the thick field oxide film 106 is formed over the regions where there are not transistors. A wiring layer, for instance, can be formed over the thick field oxide film 106, so that the regions covered by the field oxide film 106 is formed can be used as wiring channels.

The emitter region 118 can be formed by implanting n-type impurities into the main surface of the substrate, without forming the polycrystalline silicon electrode 119, and the collector contact region can be formed after the base region and the emitter region have been formed.

The field oxide film 106 for the wiring region may be formed simultaneously with the formation of the silicon oxide film 109 in the U-groove, in the same way as the formation of the isolation oxide film 110.

An isolation oxide film (an insulating material providing isolation) is formed between the collector contact region and the base region simultaneously with the formation of an oxide film (insulating material) in the U-grooves used for isolation. Therefore, the isolation oxide film (the insulating material providing isolation) between the collector contact region and the base region has a nearly uniform thickness from the central portion to the edge portions, so that the base region and the collector region are completely isolated from each other, and the thickness of the isolation oxide film (the insulating material providing isolation) does not vary much, and consequently, the transistors exhibit an improved performance. Moreover, there is no need for providing a separate step of forming an isolation oxide film between the collector contact region and the base region, and the process can thus be simplified.

The present invention accomplished by the inventors has been described in the foregoing by way of a specific embodiment. However, the invention should in no way be limited to this embodiment alone, but can be modified in various ways within a range that does not depart from the gist of the invention.

For instance, the field oxide film provided over the wiring region in this embodiment need not be limited to one that is formed by the isoplanar technique. The field oxide film can be obtained by selective oxidation, without subjecting the surface of the semiconductor substrate to etching. A p⁺ -type buried layer can be formed just under the field insulation film, or the field insulation film need not be formed at all.

The foregoing description has dealt with the case in which this aspect of the present invention was adapted to a bipolar type semiconductor integrated circuit, which was used as a background for the invention. This aspect of the present invention, however, should not be limited to this embodiment alone, but can be utilized for any semiconductor device that requires isolation regions on the main surface of a semiconductor substrate. For example, the present invention can also be used for forming MOS devices, particularly CMOS devices. For example, the trench can be utilized to isolate P(N)-well (substrate) and N(P)-well (substrate), and film 110 can be used to isolate each MOSFET. Also, the present invention can be applied to devices provided with both MOSFETs and a bipolar transistor.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to one having ordinary skill in the art and we therefore do not wish to be limited to the details shown and described herein, but intend to cover all such modifications a are encompassed by the scope of the appended claims. 

What is claimed is:
 1. A semiconductor integrated circuit device having a plurality of active regions in a semiconductor substrate, in which active regions a number of semiconductor elements are formed, and an inactive region in the semiconductor substrate, the inactive region having located thereon wirings, the wirings being connected to at least one of said number of semiconductor elements, with the inactive regions being positioned adjacent one of said plurality of active regions, comprising:(a) the semiconductor substrate, having a main surface; (b) a pair of grooves formed in the semiconductor substrate, each groove of the pair of grooves being formed so as to extend from said main surface into the semiconductor substrate, the pair of grooves defining said inactive region therebetween, the pair of grooves having groove surfaces in the substrate extending from said main surface into the substrate; (c) a single first insulating member formed on the groove surfaces of the pair of grooves, and a second insulating member extending on said semiconductor substrate, on said inactive region, between said pair of grooves, the first insulating member, on the grooves surfaces of the pair of grooves, including a silicon oxide film formed on the groove surfaces and a silicon nitride film formed on the silicon oxide film, and the second insulating member, on the inactive region, including an insulating film of a sufficient thickness for suppressing a parasitic capacitance of said wiring below a predetermined level; (d) a polycrystalline silicon body filling each groove of said pair of grooves such that each of said pair of grooves includes the silicon oxide and silicon nitride films and said body of polycrystalline silicon; and (e) said wirings, located on said inactive regions such that said second insulating member is interposed between the inactive region and the wirings.
 2. A semiconductor integrated circuit device according to claim 1, wherein the semiconductor substrate is a silicon substrate.
 3. A semiconductor integrated circuit device according to claim 2, further comprising an isolation region formed in at least one of said plurality of active regions.
 4. A semiconductor integrated circuit device according to claim 3, wherein said isolation region includes a silicon oxide layer formed in said at least one of said plurality of active regions.
 5. A semiconductor integrated circuit device according to claim 4, wherein the silicon oxide layer has a thickness substantially the same as that of the first insulating member formed on the groove surface of the pair of grooves.
 6. A semiconductor integrated circuit device according to claim 3, wherein said isolation region is a groove, formed in said at least one of said plurality of active regions, filled with a filling material.
 7. A semiconductor integrated circuit device having a plurality of active regions in a Si substrate, in which active regions a number of semiconductor elements are formed, and an inactive region in the Si substrate, the inactive region having located thereon wirings, the wirings being connected to at least one of said number of semiconductor elements, with the inactive region being positioned adjacent one of said plurality of active regions, comprising:(a) the Si substrate, having a main surface; (b) a pair of grooves formed in the Si substrate, each groove of the pair of grooves being formed so as to extend from said main surface into the Si substrate, the pair of grooves defining the inactive region therebetween, the pair of grooves having groove surfaces in the substrate extending from said main surface into the substrate; (c) a first insulating member formed on surfaces of each groove of said pairs of grooves, and a second insulating member extending on said Si substrate, on said inactive region, between said pair of grooves, said first insulating member including a silicon oxide film adjacent the groove surfaces and a silicon nitride film adjacent the silicon oxide film, the second insulating member including an insulating film of a sufficient thickness for suppressing a parasitic capacitance of said wiring below a predetermined level; (d) a polycrystalline silicon body filling each groove of said pair grooves such that each of said pair grooves includes the silicon oxide and silicon nitride films and said body of polycrystalline silicon; and (e) said wirings, located on said inactive region such that said second insulating member is interposed between the inactive regions and the wirings.
 8. A semiconductor integrated circuit device according to claim 7, further comprising:second and third insulating films formed on said polycrystalline silicon body.
 9. A semiconductor integrated circuit device according to claim 8, wherein said second insulating film is made of silicon oxide and said third insulating film is made of silicon nitride and wherein the thickness of said second insulating film made of silicon oxide is larger than the thickness of the silicon oxide film of the first insulating member.
 10. A semiconductor integrated circuit device according to claim 7, further comprising:second and third insulating films formed on said polycrystalline silicon body and on said inactive region.
 11. A semiconductor integrated circuit device according to claim 10, wherein said second insulating film is made of silicon oxide and said third insulating film is made of silicon nitride and wherein the thickness of said second silicon oxide film is larger than that of said silicon oxide film.
 12. A semiconductor integrated circuit device according to claim 11, wherein said semiconductor integrated circuit device includes MOSFETs.
 13. A semiconductor integrated circuit device according to claim 11, wherein said Si substrate includes a collector buried layer formed on an Si body, wherein said semiconductor integrated circuit device includes bipolar devices, and wherein said pair of grooves extend through said collector buried layer of said silicon substrate.
 14. A semiconductor integrated circuit device according to claim 7, wherein the Si substrate further comprises:a collector buried layer formed in a surface region of a Si body of said Si substrate; and a Si epitaxial layer formed on said collector buried layer, said collector buried layer being cut by said pair of grooves, said pair of grooves extending from a surface of said Si epitaxial layer to said Si body.
 15. A semiconductor integrated circuit device according to claim 7, wherein a further groove, shallower than said pair of grooves, is provided between said pair of grooves, said semiconductor integrated circuit device further comprising a further polycrystalline silicon body filling up said further groove.
 16. A semiconductor integrated circuit device according to claim 7, further comprising an insulating film formed on the surface of at least one of the plurality of the active regions, and wherein said insulating film has a plurality of openings and has a portion thicker than other portions thereof.
 17. A semiconductor integrated circuit device according to claim 16, wherein said member of semiconductor elements include a bipolar transistor provided in said at least one of the plurality of the active regions, and wherein said portion thicker than other portions thereof is provided between a base region and a collector contact region of said bipolar transistor.
 18. Semiconductor substrate, for forming an integrated circuit device, comprising:(a) a semiconductor body having a main surface; (b) a plurality of pairs of grooves formed in said semiconductor body, extending from said surface into said semiconductor body, exposing surfaces of the semiconductor body, each pair, of said plurality of pairs of grooves, having sandwiched therebetween, in the semiconductor body, an inactive region, and with active regions being provided in portions of the semiconductor body other than portions thereof having the inactive regions; (c) a continuous isolation oxide layer, formed on surfaces of the semiconductor body exposed in each of the grooves of the plurality of pairs of grooves, and on said main surface of the semiconductor body in the inactive regions; (d) a silicon nitride layer formed on said isolation oxide layer in each of the grooves of the plurality of pairs of grooves; and (e) a polycrystalline silicon filling up each of the grooves, with a silicon oxide layer formed on top of the polycrystalline silicon.
 19. A semiconductor substrate according to claim 18, wherein the semiconductor body is formed of silicon, and the first continuous isolation oxide layer is a silicon oxide layer.
 20. A semiconductor integrated circuit device comprising:(a) a semiconductor body having a main surface; (b) a plurality of pairs of grooves formed in said semiconductor body, extending from said main surface into said semiconductor body, exposing surfaces of the semiconductor body, each pair, of said plurality of pairs of grooves, having sandwiched therebetween, in the semiconductor body, an inactive region, with active regions being provided in portions of the semiconductor body other than portions thereof having the inactive regions; (c) a first isolation oxide film formed on surfaces of the semiconductor body exposed in each of the grooves of the plurality of pairs of grooves, and on said main surface of the semiconductor body in the inactive regions; (d) a silicon nitride layer formed on said first isolation oxide film in each of said grooves; and (e) a second isolation oxide film over a portion of at least one of the active regions so as to define first and second sub-regions of said at least one of the active regions, with the first sub-region being a first conductivity type and the second sub-region being of a second conductivity type opposite to the first conductivity type, the second isolation oxide film constituting an electrical isolation member between the first and second sub-regions.
 21. A semiconductor integrated circuit device according to claim 20, further comprising a wiring for said integrated circuit device, said wiring being provided over the first isolation oxide film on the inactive regions so that said first isolation oxide film separates the wirings from the semiconductor body to minimize parasitic capacitance between the wirings and semiconductor body.
 22. A semiconductor integrated circuit device according to claim 20, wherein the first and second isolation oxide films are films formed simultaneously with each other.
 23. A semiconductor integrated circuit device according to claim 1, wherein said inactive region is positioned between a pair of active regions of said plurality of active regions.
 24. A semiconductor integrated circuit device according to claim 1, wherein said wirings are disposed on the insulating film of said second insulating member, on said inactive region, and extend along said inactive region.
 25. A semiconductor integrated circuit device according to claim 24, wherein said insulating film of the second insulating member is formed of silicon oxide, and wherein said wirings are disposed directly on the silicon oxide of said insulating film of the second insulating member.
 26. A semiconductor integrated circuit device according to claim 1, wherein said insulating film of said second insulating member, on said inactive region, is a silicon oxide film, of a thickness larger than that of the silicon oxide film formed on the groove surfaces of the pair of grooves.
 27. A semiconductor integrated circuit device according to claim 1, wherein said insulating film of said second insulating member, on the inactive region, includes a silicon oxide sub-film, provided on the inactive region, and a silicon nitride sub-film provided on the silicon oxide sub-film, the total thickness of the silicon oxide and silicon nitride sub-films being sufficient so as to suppress the parasitic capacitance of the wirings below the predetermined level.
 28. A semiconductor integrated circuit device according to claim 8, wherein the second insulating film, of said second and third insulating films, is a silicon oxide film, formed on the polycrystalline silicon body, and the third insulating film is a silicon nitride film, formed on the silicon oxide film formed on the polycrystalline silicon body.
 29. A semiconductor integrated circuit device according to claim 7, wherein the insulating film of said second insulating member is a silicon oxide film, and said wirings are provided directly on the silicon oxide film of the insulating film of the second insulating member.
 30. A semiconductor integrated circuit device according to claim 18, wherein each of the active regions and the inactive regions has an upper surface, corresponding to the main surface of the semiconductor body, the upper surface of each active region and each inactive region being substantially in the same plane. 